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GC/MS short vacuum drop after injection
Posted: Sat Aug 11, 2012 11:52 pm
by adsfo
Is it normal to have a short (one second) vacuum drop about 30 sec after injection? My typical vacuum is 3x10-5 and it rops to 3x10-4 about 30s after the injection (splitless) then comes back down to normal within 1s.
Re: GC/MS short vacuum drop after injection
Posted: Sun Aug 12, 2012 2:23 am
by Don_Hilton
Sounds like the solvent passing from the column and through the mass spectrometer on its way out throgh the pump. Check your linear velocity on the colulmn and the length of the column. This will give you an estimate of the dead time. This spike in pressure will be at or just after the dead time.
Re: GC/MS short vacuum drop after injection
Posted: Mon Aug 13, 2012 3:42 pm
by cleh
Do you have a delay time in your method that keeps the multiplier and filament off until the solvent passes through? If not, it's a good idea to add one to increase the life of the multiplier and filament.
Re: GC/MS short vacuum drop after injection
Posted: Fri Aug 17, 2012 6:50 pm
by Rick
Yes...it is normal (solvent )
Re: GC/MS short vacuum drop after injection
Posted: Sat Aug 25, 2012 2:28 am
by thohry
It's due to the solvent expansion. If it's too severe, you can inject less and/or use n-hexane instead of MeOH or ACN (just if). Remember to use solvent delay.